The present invention relates to a cleaning processing method of a film forming apparatus.
In general, a semiconductor integrated circuit comprised of a number of circuit elements is formed on a substrate such as a silicon substrate or the like by repeating film forming processing and pattern etching processing.
In manufacturing steps thereof, metal wires connecting circuit elements with each other, contact metals making electric contacts with circuit elements, and barrier metals for preventing diffusion of Si from the substrate all preferably have a low electric resistance and are also preferably made of materials having an excellent corrosion-resistance.
Ti (titanium), W (tungsten), Mo (molybdenum), and the like are selected as those materials. In particular, a Ti film has an excellent characteristic such as an electric characteristic, a corrosion-resistance, and the like and is therefore used in many cases.
For example, in case of forming a Ti film by a CVD method using a CVD (Chemical Vapor Deposition) apparatus, film formation is carried out by plasma processing in an atmosphere in which a TiCl.sub.4 (titanium tetrachloride) gas and a H.sub.2 gas are introduced as material gases.
Not only in film formation of a Ti film but also in film formation on a wafer surface by a CVD apparatus, an unnecessary film inevitably sticks to the side wall of a process chamber, surfaces of a susceptor (or mount table), a shower head which supplies a material gas, and the like.
If such an unnecessary film is peeled off during film formation on a semiconductor wafer, the peeled film becomes particles which stick to the semiconductor surface while film formation is being performed, thereby causing a factor of a defective element. Therefore, cleaning processing for removing a film formed on and sticking to inner structural components and the like is sequentially performed on a certain number of wafers, e.g., twenty five.
Generally, in the cleaning processing of an unnecessary Ti film, a semiconductor wafer on which a Ti film is formed is conveyed out of a process chamber. Thereafter, the temperature of the process chamber is decreased to about 200 to 300.degree. C. which is preferred as a cleaning temperature, from about 650.degree. C. which is a film forming temperature of a Ti film. After the temperature reaches the cleaning temperature, the ClF.sub.3 gas, NF.sub.3 gas, and the like are introduced to a processing chamber and cleaning processing is carried out.
In case of using a ClF.sub.3 gas, electric discharging is stopped to prevent generation of a plasma (hereinafter called plasmaless cleaning processing). In case of using a NF.sub.3 gas, a plasma is generated (hereinafter called plasma cleaning processing).
The temperature in the process chamber is decreased to 200 to 300.degree. C. when carrying out cleaning processing as described above, because not only unnecessary Ti films but also inner walls of the process chamber and the surfaces of the susceptor are removed if the temperature in the process chamber is too high.
After the cleaning processing is thus completed in a predetermined time period, the temperature in the process chamber is increased again, for example, to 650.degree. C., and formation of a Ti film is continued.
FIG. 6 shows the temperature in the process chamber in film forming steps according to a conventional CVD method.
In the film forming steps, the period Ti is a film forming processing step in which the temperature in the processing chamber is set to 650.degree. C. which is the film forming temperature. In this step, for example, film formation of Ti films is performed sequentially on twenty five semiconductor wafers in an atmosphere in which material gases as described above are introduced.
Upon completion of the film formation, the processing flow goes to a cleaning processing step. At first, the temperature is decreased from 650.degree. C. to 250.degree. C. in a period T2. After the temperature reaches the cleaning temperature, a ClF.sub.3 gas, a NF.sub.3 gas, and the like are introduced into the process chamber in a period T3 and cleaning processing is performed on the Ti films.
Upon completion of the cleaning processing, the temperature in the process chamber is increased to 650.degree. C., and the cleaning processing step is completed.
Further, the processing flow further goes again to a film forming processing step and Ti films are formed on a semiconductor wafer, like in the period Ti.
Thus, the film forming processing step (corresponding to the period Ti) and the cleaning processing step (corresponding to the periods T2 to T4) are repeatedly carried out.
In a conventional cleaning processing step as described above, the temperature of the chamber must be increased and decreased before and after the cleaning processing in the period T3, e.g., in the periods T2 and T4, as shown in FIG. 6. Therefore, film forming processing cannot be carried out during the periods T2 and T4, and as a result, a problem occurs in that the throughput is decreased.
Although depending on the number of wafers to be subjected to film forming processing, for example, each of the period T2 for decreasing the temperature and the period T4 for increasing the temperature requires about thirty minutes with respect to the period T3 of the cleaning processing of about thirty minutes, so that the time required for the cleaning processing step finally occupies ninety minutes, thereby causing a significant factor which decreases the throughput.
In addition, since the increase and decrease of the temperature are repeatedly carried between the film forming temperature and the cleaning temperature, there is a drawback that metal fatigue is accumulated in structural components inside a chamber, such as a mount table or the like, and the life-time of the structural components and the like are shortened.
Further, in plasma cleaning processing using a NF.sub.3 gas, it is impossible to sufficiently remove films formed on and sticking to portion other than the region where a plasma is formed, e.g., films sticking to side surfaces of a shower head.